Prior art pitch sensors have included stroboscopes and oscilloscopes to effect the pitch sensing/instrument tuning functions. Also, as is well known, tuning forks have also been used to effect the instrument tuning function.
For example, Long U.S. Pat. No. 2,584,277 entitled "Electronic Tuning Device" discloses a device for producing two precise frequences such as A at 440 H.sub.z and B flat for use primarily as a reference for orchestra tuning. The output of such device is either audio or a strobe disc;
Krauss U.S. Pat. No. 2,806,953 entitled "Electronic Oscillator for Producing Frequencies of Musical Tones" discloses a device wherein reference frequency tones covering one octave of the equally tempered musical scale are generated for comparison with tones picked up from the musical instrument. In such device, comparison is made using a synchronously driven strobe disc;
Peterson U.S. Pat. No. 2,924,776 entitled "Tuner" discloses a device wherein reference frequency tones covering one octave of the equally tempered musical scale are generated for the highest octave. Tandam 2:1 dividers are provided to cover the lower octaves. These tones are compared with corresponding tones picked up from the musical instrument with or without added diode distortion and made audible by beats from a loud speaker;
Poehler U.S. Pat. No. 2,958,250 entitled "Musical Instrument Tuning Apparatus" discloses a device wherein reference frequency tones covering one octave are arranged to give a circular pattern to an oscilloscope. Tones from a musical instrument are made to generate light and dark segments in the circular pattern which are stationary or rotate in one direction or the other depending on relative tone conditions;
Schott U.S. Pat. No. 3,472,116 entitled "Device for Producing Frequency Intervals For Tuning Musicals Instruments" discloses a device wherein a voltage controlled oscillator is made to lock in to a first musical instrument pitch tone picked up by a sound sensing means associated with that tone. A reference signal is then generated and relatively shifted in pitch by the 12th root of two for use in adjusting an adjacent pitch tone picked up by a second sensing means. Scalewise tuning is accomplished by successively shifting the double sensing means from each adjusted tone to the next;
Davidson U.S. Pat. No. 3,585,898 entitled "Musical Instrument Tuning Reference Standard" discloses a device wherein the standard is derived using the 60 H.sub.z power frequency divided by two, squaring the wave shape, and selecting out the 11th harmonic to obtain 330 H.sub.z, being almost the tempered reference pitch tone E for use in guitars and similiar instruments;
Freeman U.S. Pat. No. 3,688,010 entitled "Tone Modulation System" discloses a device relating to the generation of musical tones with no relation to musical instrument tuning;
Ihrke U.S. Pat. No. 3,722,353 entitled "Pitch Measurement Circuit" discloses a device whose primary use is to compare the playing of single tone musical instruments such as voice, violin, woodwinds, etc. recorded on one track of a two track tape recorder with an identical sequence of correctly played tones on the second track. A system of lights indicates whether the tones under test are above, below, or on pitch;
Sanderson U.S. Pat. No. 3,879,684 entitled "Tuneable UJT Oscillator Circuit" discloses a device using phase comparison of reference and test tones to indicate the relative pitch conditions. These are indicated in an array of lights which are sequentially lighted for off-pitch conditions and stationary lighting for the on-pitch state;
Peterson U.S. Pat. No. 3,952,625 entitled "Electronic Tuning Device" discloses a device for generating reference tones of the musical scale by downward counting from an adjustable high frequency oscillator frequency. A motor synchronously driven by these tones rotates a strobe disc for comparison with tones picked up from a musical instrument. Provision is also made for audible comparison;
Sanderson U.S. Pat. No. 3,968,719 entitled "Method for Tuning Musical Instruments" discloses a device similar to that of U.S. Pat. No. 3,879,684 but with an added tuning arrangement by which "stretch" may be taken into account;
Luce U.S. Pat. No. 3,991,645 entitled "Electronic Musical Instrument with Exponential Keyboard and Voltage Controlled Oscillator" discloses a device wherein a key selects a control voltage from an exponential voltage divider for controlling the frequency of a voltage controlled oscillator which produces a frequency which is directly proportional to the control voltage and inversely proportional to a reference voltage;
Yoshikawa U.S. Pat. No. 4,019,419 entitled "Tuning Device" discloses a device which utilizes downward counting from a high frequency oscillator to arrive at pitch tone references of the tempered scale. Provision is made for injecting into the crystal extra pulses of suitable width to provide upward or downward shifting of the reference pitch scale. Comparison is made with the musical instrument tones using a strobe disc;
Denov U.S. Pat. No. 4,023,462 entitled "Musical Instrument Tuning Device" discloses a device intended for automatic tuning of kettle drums. In such device a desired reference tone is compared to the tone from the kettle drum. The drum skin tension is automatically adjusted to match the reference tone by a motor driven servomechanism;
Merritt U.S. Pat. No. 4,028,985 entitled "Pitch Determination and Display System" discloses a device which makes use of the peaks in musical tones with measurement of time intervals between peaks as an indication of pitch;
Kondo U.S. Pat. No. 4,077,298 entitled "Apparatus for Automatically Tuning an Electronic Musical Instrument" discloses a device which provides automatic tuning of electronic musical instruments, which device employs voltage controlled oscillators as tone sources. Such device does not automatically tune standard musical instruments;
Calvin U.S. Pat. No. 4,122,751 entitled "Automatic Instrument Tuner" discloses a device which is not an automatic tuner. The automatic feature is one where the reference pitch tone closest to that coming from a musical instrument is displayed in terms of a frequency difference with lamps indicating whether this difference is above or below the reference. In such patent, mention is made of magnetic sensing but no specific device is disclosed.
It does not appear that the above cited prior art references make use of saw-tooth shaping of the type having a rapid rise or fall time followed by a slow recovery by which the instrument pitch tones are modified to give the unique sounds of the test output. It also does not appear that the above cited prior art references disclose a magnetic sensing probe for picking up or detecting vibrations such as those from piano strings.
Objects of the present invention are therefore to provide:
more accurate tuning of instruments such as a piano or other string instrument;
a pitch sensing and instrument tuning device which does not require the use of oscilloscopes, stroboscopes, or tuning forks;
an improved device to produce tones suitable for tuning musical instruments;
an improved device to generate tones suitable for tuning musical instruments and which is simple and inexpensive in construction while at the same time may be accurately calibrated;
an improved device to produce reference tones for tuning musical instruments and in which the tone pitch is not influenced by the volume or intensity of the tone produced;
an improved musical instrument tuning device having a single oscillator circuit which provides a plurality of different tones such as the 12 semitones within an octave;
an oscillator for providing a plurality of musical tones wherein the oscillator can be tuned so that the tones have precise values without affecting the frequency relationship of the different tones produced by the oscillator;
an improved musical instrument tuning device which accurately generates signals of frequencies related to the frequencies of tones to be checked and gives an audible indication of the deviation of the tones tested with respect to the correct frequencies therefor;
a tuning apparatus which permits tuning of conventional musical instruments in a musically perfect way and wherein tuning errors due to wrong control are prevented;
an improved tuning device having accuracy and stability;
an improved tuning device which can operate an audio frequency pitch standard for audible comparison with an instrument to be tuned;
a tuning device which is readily adapted for tuning a wide variety of instruments; and
a musical instrument tuning device which may be easily controlled by a musician or a non-technical operator.